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Site Investigation of Ground Water

Christina PageNew Jersey Department of Environmental Protection

Bureau of Inspection and Review

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Ground Water Site Investigation Overview

• Applicable Ground Water Remediation Standards

• How to Conduct a Ground Water SI

• Background Ground Water Investigations

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Purpose of a Site Investigation

Determine if remediation is necessary:

• Because contaminants are present at the site or AOC; or

• Because contaminants have emanated or are emanating from the site or AOC; and

• Levels are above any of the applicable remediation standards or criterion

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Remediation Standards

• The Remediation Standards, N.J.A.C. 7:26D establish the GWQS as the minimum standards

• The GWQS at 7:9C identifies three ground water designations

• Use or develop the standard that is applicable to the ground water designation

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How to Conduct a SI

• Sample locations

• Frequency of sampling

• Data collection

• Important to minimize cross contamination

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How to Conduct a SI - Sampling Locations

• Bias both vertically and horizontally to suspected location of greatest contamination– Contaminant type– AOC history– Location of discharge– Instrument readings or other field indicators

(i.e., visual)– Age of discharge

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How to Conduct a SI - Sampling Locations

If samples cannot be biased due to access limitations:

• Collect multiple ground water samples surrounding the AOC

OR• Collect as close to and down gradient from the AOC as

practical-– Collect down gradient from AOC by predicting GW flow

• Topographic relief• Location of surface water• Pumping well• Subsurface conduits• Adjacent sites• Install temporary or permanent wells

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How to Conduct a SI - Data Collection

• Log soil cores at each boring location

• Use consistent and approved soil classification systems

• Assists in development of conceptual hydrostratigraphic model

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How to Conduct a SI - Vertical Biasing

For contaminants less dense than water:

• Screen soil cores through the water table to account for contamination trapped beneath the water table

• Bias ground water sample to zone of greatest contamination identified during field screening

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LIF Image Showing Free and Residual NAPL Relative to the Water Table

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How to Conduct a SI - Vertical Biasing

For DNAPL contaminants:

• Advance core below the water table until:

–The first indication of contamination OR

–The first low permeability strata OR

–The top of bedrock

• If you encounter bedrock above the water table, sample first ground water in bedrock

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Sample Here

Readings on Field Instrumentation

Low permeability strata or top of bedrock

Unconsolidated Sand

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Sample Here

No Readings on Field Instrumentation

Low permeability strata or top of bedrock

Unconsolidated Sand

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Site Investigation Conclusion

Whenever contamination is identified in the site investigation…proceed to the remedial investigation

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Background Ground Water Quality Investigation

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Why Conduct a Background Ground Water Quality

Investigation?

All or part of the contamination identified onsite may be the result of contamination originating from:

• An off-site source; or

• Natural background

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Off-Site Source of Ground Water Contamination Overview

• Scope of background investigation

– Will depend on site complexity

– Differentiate on-site vs. off-site contribution

– Outcome needs to be technically justifiable

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Scope of Background Investigation

• Site complexity may warrant

– Multiple sampling points

– Multiple sampling events

– Multiple water bearing zones

– Tailor analysis to contaminants of concern, including parent/degradation products

– Collect hydrogeologic data to support conclusion

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Scope of Background Investigation

• Understand on-site contribution

– Conducting a comprehensive PA

– Identify all areas of concern SI

– Delineating source areas RI

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Scope of Background Investigation

• We acknowledge that your role has shifted…– From DEP driving decisions

– To LSRPs driving decisions

• Outcome needs to be technically justifiable

– Consider that the site “next door” may hire a LSRP to critique the conclusions of your investigation

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Ground Water Remediation Requirements

• No ground water remediation is necessary when:– The contaminant was never used on the site

– The contaminant was never discharged on the site

– The contaminant is present in the background samples

Call the DEP Hotline to report the upgradient, unknown source contamination

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Ground Water Remediation Requirements

• If there has been a site related discharge, no further ground water remediation is necessary when: − All site related contamination

associated with the AOC has been remediated, and

− Contaminant concentrations are greater in the upgradient ground water

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Ground Water Remediation Requirements

• Further remediation is required when:

– There has been site related discharge

AND

– On-site ground water contaminant concentrations are greater than concentrations coming on to the site

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Ground Water Remediation Standard

• The Ground Water Remediation Standard is the higher of:

– The Ground Water Quality Standard for the contaminant

or – The background concentration of the

contaminant

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GWRS Based on Background

• Background ground water concentration may change over time

• Re-evaluate background contaminant concentrations at a regular frequency

• Revise the site specific ground water remediation goal based on current background concentrations

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Natural Background

• Support natural background based on:– The composition of the formation

– The ubiquitous distribution of the constituents

– No elevated concentrations at AOCs

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Natural Background Requirements

• No discharge:– No remediation required– No CEA or remedial action permit required

• Discharge has occurred:– Remediate– CEA and remedial action permit may be

required